1. Field
The field of the invention is carpenters' aid devices, and more particularly such devices for preparatory marking for installation of structural members.
2. State of the Art
In wood frame building construction, wall studs, joists, rafters and other components must often be installed at regularly spaced intervals along a straight line. The marking of a straight line between widely spaced points is typically done by using a chalk dust impregnated cord, stretched along a base member or the like providing a working surface between the points. The cord is snapped against the working surface, leaving a temporary straight line of chalk dust. Intervals along this line are then marked with pencil and carpenter's ruler, flexible tape or the like. However, in some instances, the chalk line cord has been modified to produce the spacing marks directly. U.S. Pat. No. 4,152,836 discloses a chalk line marker cord having a metal wire core covered by a flexible sleeve. The sleeve material is smooth and otherwise adapted to be resistant to retention of chalk dust. At intervals along the cord, the chalk resistant sleeve is discontinued for a short distance to be replaced by short segments of material adapted to retain the chalk. Use of this cord is intended to produce a line of correctly spaced marks along the working surface. The desired intervals are indicated by reference to the ends of the marks deposited upon the working surface. However, these marks tend to be less than precisely defined. The points of transition from chalk to bare surface tend to vary considerably. Extraneous marks also occur from chalk adhering in unwanted sites even along the smooth sleeve. Another troublesome factor is non-uniform chalking in the chalk retaining sections.
A British Patent No. 1,026,051 discloses an interval marking chalk line having chalk retention resistant sleeves, of gloss paint, e.g., at intervals. The marked line thus has spaced interruptions, rather than spaced marks as with the above discussed device. However, the same basic shortcomings exist. Any non-uniformity in the chalking of the sections leads to confusing markings by spurious interruptions of the line in the case of the British Patent, or by equally spurious extraneous marks with the U.S. patent.
Some of the above shortcomings tend to be countered by another device, disclosed in U.S. Pat. No. 4,679,325, albeit with increased complexity and cost. A flat tape, generally resistant to chalk, is used, which has perforations at the required intervals. A chalk impregnatable felt strip is provided on the side of the tape away from the working surface. The perforations allow the chalk to be deposited upon the working surfaces through these regularly spaced perforations. The tape may be less stretchable than the small wire cord with the other devices discussed herein. This contributes to accuracy in the location of the interval marks. Since the chalk carrying cloth is held away from actual contact with the working surface, the deposit of the chalk dust therethrough may be unreliable. The tape, as in the case of the wire sheath, does not completely reject deposits of chalk. With all these prior art devices, confusing unplanned marks may occur. All may produce imprecisely defined marks. Clearly, there is a need for a chalk interval marking device which avoids extraneous marks and reliably produces well defined interval marks. No prior art device provides for the contact of the working surface by only the portion of the line adapted to provide the marks to prevent the occurrence of extraneous marks.